This invention relates generally to the regulation of combustion in a radiant infrared burner. Radiant burners are used in a variety of applications including space and water heating systems. In particular, the invention relates to a method of modulating the surface area of a radiant burner on which combustion occurs as a function of the heat output rate of the burner and to an apparatus to effect such modulation.
Radiant infrared burners operate most effectively when the heat flux on the surface of the burner is maintained at some optimum level. The value of this optimum heat flux level is a function of the physical configuration of the burner, the materials used in its construction and the type and composition of the combustible gas used as a fuel.
Designers usually plan for the optimum burner surface heat flux level to exist when the burner is operating at or near its maximum rated heat output capacity. Many applications, however, require heat sources that can deliver variable heat output rates. This requirement means that a radiant burner used in such an application will operate at least part of the time at a heat output rate that will result in a surface heat flux level that is at some value less than optimum.
Radiant burner operation generally remains satisfactory even when the surface heat flux level is as low as 50 percent of the optimum value if the proper ratio of fuel gas to combustion air in the combustible gas supplied to the burner is maintained. At still lower surface heat flux levels, however, burner performance is severely degraded, as the burner produces unacceptable levels of carbon monoxide as a combustion product. At very low surface heat flux levels, radiant burners exhibit even more undesirable performance characteristics such as ignition delays and other combustion problems.
In order to adapt a radiant infrared burner for use in an application requiring it to produce a heat output rate that varies over a wide range of values within its design capacity, it is necessary therefore to maintain the heat flux on the surface of the burner at an acceptable level even at a very low relative heat output rate.